Birefringent Substrate Research Articles

Controlling asymmetric transmission phase in planar chiral metasurfaces

AbstractMetasurfaces with ultrathin artificial structures have attracted much attention because of their unprecedented capability in light manipulations. The recent development of metasurfaces with controllable responses opens up new opportunities in various applications. Moreover, metasurfaces composed of twisted chiral structures can generate asymmetric responses for opposite incidence, leading to more degrees of freedom in wave detections and controls. However, most past studies had focused on the amplitude responses, not to mention using bi-directional phase responses, in the characterization and light manipulation of chiral metasurfaces. Here, we report a birefringent interference approach to achieve a controllable asymmetric bi-directional transmission phase from planar chiral metasurface by tuning the orientation of the metasurface with respect to the optical axis of an add-on birefringent substrate. To demonstrate our approach, we fabricate planar Au sawtooth nanoarray metasurface and measure the asymmetric transmission phase of the metasurface placed on a birefringent sapphire crystal slab. The Au sawtooth metasurface-sapphire system exhibits large oscillatory behavior for the asymmetric transmission phase with the tuning parameter. We confirm our experimental results by Jones matrix calculations using data obtained from full-wave simulations for the metasurface. Our approach in the characterization and light manipulation of metasurfaces with controllable responses is simple and nondestructive, enabling new functionalities and potential applications in optical communication, imaging, and remote sensing.

Plasmonic gold nanodiscs using piezoelectric substrate birefringence for liquid sensing

This article presents the simulation, fabrication, and experimental characterization of a surface plasmonic resonance (SPR) sensor integrated with an acoustic sensing compatible substrate. The SPR sensor is designed to work in the visible region with gold nanodisc arrays fabricated on LiNbO3, which is both piezoelectric and birefringent. A linear relationship between resonance wavelength and varying liquid refractive indices were observed in experiments, and a sensitivity of 165 nm/refractive index unit was obtained. Polarization effects of the birefringent property of the Y-cut LiNbO3 substrate have been investigated, which can also be applied to X-cut LiNbO3. Our study demonstrates the feasibility of an SPR sensor device utilizing a birefringent substrate, which has acoustic wave compatibility and can pave the way toward much more robust and flexible biosensing devices.

Phase modulator birefringence effect on multibound soliton formation in an active mode-locked fiber laser

Multibound solitons generated in an active mode-locked fiber ring resonator can be considered to offer some significant applications in the coding for optical packet transmission. Optical phase modulators (PMs) incorporated in such fiber ring resonators are fabricated in uniaxial birefringent crystal substrate and thus influence both polarized modes of a coupled linearly polarized mode from a weakly guiding fiber forming the ring. Thus there are two polarized rings in such a structure of the active mode-locked fiber ring resonators. They are coupled and interact with each other in the generation of multibound solitons. This paper thus studies the influence of two types of electrodes for phase modulation, lumped and traveling wave, in such birefringent fiber active ring resonators, and hence the transitional formation of multibound solitons. It is shown that there exist comblike spectral components in the ring cavity due to the birefringence property of the PM. Furthermore, the narrow free spectral range of the ring resonator limits the pulse shortening and hence the formation of the multibinding of solitons.

Interpretation of transmission through type II superconducting thin film on dielectric substrate as observed by laser thermal spectroscopy

We provide a thorough analysis of THz properties of BCS-like superconducting thin films. Temperature and frequency dependence of complex conductivity in zero magnetic field is discussed by utilizing the Zimmerman et al. explicit BCS based formula [Physica C 183 (1991) 99]. We extend this approach by employing the effective medium theory and develop a phenomenological model capable of accounting for the influence of external magnetic field. Using Yeh powerful formalism [Surface Sci. 96 (1980) 41] we calculate optical transmission of linearly polarized laser beam normally incident to a multilayered sample consisting of a thin NbN film grown on birefringent sapphire substrate, entirely covering ranges of interest in temperature and frequency. A proposal to exploit linear polarization of the incident beam parallel with principal axes of conductivity tensor is explained and theoretical predictions for a realistic NbN sample are computed and discussed.

Terahertz thermal spectroscopy of a NbN superconductor

We report far-infrared optical properties of a NbN superconductor. Transmission through a high-quality NbN film grown on a birefringent sapphire substrate above and below its superconducting transition down to the zero-temperature limit is measured at six different frequencies from 0.4 to 2.5 THz both above and below its optical gap. The experimental results agree with theoretical calculations developed based on utilization and extension of the BCS model of Zimmermann et al. [Physica C 183, 99 (1991)] applied for the NbN film. Full quantitative agreement over the entire ranges of temperature and frequencies is found based solely on the physical properties of this NbN film sample and on the parameters of an identical sapphire substrate as measured in time-domain spectroscopy experiments, without use of any additional fitting parameters.

LONG-RANGE SURFACE PLASMONS ON HIGHLY ANISOTROPIC DIELECTRIC SUBSTRATES

We calculate the propagation length of surface plasmons in metal-dielectric structures with anisotropic substrates. We show that the Joule losses can be minimized by appropriate orientation of the optical axis of a birefringent substrate and that the favorable orientation of the axis depends on ω. A simple Kronig-Penney model for anisotropic plasmonic crystal is also proposed.

In-situ characterization of metal clusters supported on a birefringent substrate using reflectance difference spectroscopy

Reflectance difference spectroscopy has been applied for the in-situ characterization of the growth of Ag cluster films on insulating birefringent Al2O3 $(10\overline{1}0)$ substrates in the spectral range of 1.5–5 eV. Information on the individual cluster, cluster film morphology and growth are derived from the anisotropy of the in-plane plasmon resonances in comparison with scanning electron microscopy images. In particular, the evolution of the dipolar resonance has been attributed to two distinct stages of coarsening involving particle aggregation and ripening, and to the development of anisotropic particle shapes for higher Ag coverages. The effect of the formation of anisotropic electrostatic images in the birefringent substrate is used to explain the spectra even in the absence of structural anisotropies.

Optical anisotropies of metal clusters supported on a birefringent substrate

We report on the optical properties of Ag nanoparticles supported on an insulating, birefringent substrate for nominal film thicknesses of less than 4 nm. Spectroscopic ellipsometry (SE) and reflectance-difference spectroscopy (RDS) were employed to detect out-of-plane and in-plane anisotropies of particle-plasmon resonances, respectively. Quantitative agreement between measured and calculated spectra is achieved using the morphological parameters determined independently from electron microscopy images. The substrate birefringence allows the detection of cluster layers by RDS via the screening of the substrate signal proportional to the layer susceptibility. In addition, an intrinsic lateral anisotropy, which is explained by the lifting of the degeneracy of planar modes due to the anisotropic images forming in the substrate, has been detected. For higher coverages the influence of anisotropic cluster shapes and strong multipolar resonances are identified.

Guided wave electrooptic and acoustooptic tunable filter apparatus and method

A two-port guided wave tunable filter in a birefringent electrooptic and/or acoustooptic substrate material includes two 3-port, symmetric Y-branch beam splitters connected by two waveguide sections in which phase-matched polarization coupling occurs, with an input port and an output port. The optical path difference between the beam splitters is half an optical wavelength, and the polarization coupling regions between the beam splitters are relatively displaced by an odd integral multiple of half the spatial period of the perturbation responsible for the coupling. In one embodiment, an electrooptic tunable filter, the polarization coupling in the waveguides is caused by a spatially periodic strain-inducing film and tuning results from an applied electric field. In another embodiment, an acoustooptic tunable filter, polarization coupling results from a surface acoustic wave and tuning is accomplished by changing the acoustic frequency. Alternatively, four port electrooptic and acoustooptic tunable filters are formed by replacing the 3-port beam splitters with 4-port directional couplers, where in each of the directional couplers the splitting ratio for TE input polarization plus the splitting ratio for TM input polarization is substantially equal to one.

Heat flux distribution on a substrate in capacitively coupled radio-frequency discharges

This letter investigates the heat flux distribution on a substrate in capacitively coupled radio-frequency argon glow discharges. The heat fluxes were determined from substrate temperature distributions measured by a high-sensitivity laser interferometer method with a LiNbO3 birefringent substrate. This method is based on monitoring the variation of refractive index with temperature. The distribution was obtained by sliding the 1-cm long LiNbO3 substrate between two semicircular glass substrates placed on a disk electrode, 12 cm in diameter. The gap length was fixed at 2 cm and gas pressure was 100 mTorr. For the substrate placed on the powered electrode, the heat flux increases radically from the glow center to the radial electrode edge from 40 to 58 mW/cm2. The heat flux toward the grounded electrode increases radically from 15 to 21 mW/cm2. The total measured heat flux to the electrode is in good agreement with electrical power consumption determined from voltage and current measurements. The radial electron density profile in the discharge chamber was measured using a Langmuir probe. The results show that the maximum electron density observed at the electrode edge coincides with the maximum heat flux.

Determination of heat and ion fluxes in plasma immersion ion implantation by in situ measurement of temperature using laser interferometry

Temperature rises of a birefringent substrate (LiNbO 3) with repetitive negative pulse bias have been measured in a capacitively coupled RF argon plasma. The measurement method is based on monitoring the variation in natural birefringence due to the changed temperature by interferometry. Using this method, the dependence of the substrate temperature rise upon the repetition rate of the pulse bias has been investigated. A negative bias of −800 V was applied in a series of pulses with repetition rates of 400–800 Hz and a duration of 35 μs using a pulse modulator. The heat flux increases with the repetition rate of the bias pulse. At 800 Hz the value is nearly equal to 40% of the power applied to the pulse modulator.

Methods and Concerns of Compensating In-Plane Switching Liquid Crystal Displays

It is well known that uncompensated in-plane switching (IPS) liquid crystal displays (LCDs) have much better viewing angle than conventional twisted-nematic (TN) LCDs. However, to achieve optimal viewing angle performance in these devices, they must be compensated by one or more films. In this paper, we will study the optimization of such compensation. We will show the benefit of using polarizers which do not have a birefringent substrate. We will also show the effect of which side of the LCD the compensation films are placed. Finally, we will investigate the surprising effect of the pretilt angle on the viewing angle of the compensated IPS LCD.

Polarization microscopy of magnetic domains for magneto-optical disks

Polarization microscopes are widely used to image the magnetic domains of a magneto-optical disk and to characterize the birefringence of the disk substrate. For high-resolution imaging, unfortunately, the coupling of the polarization rotation from the Kerr signal, the effect of Fresnel's reflection coefficients, and the substrate birefringence severely deteriorate the image contrast obtained from conventional observations. Here we present the technique of differential polarization microscopy, which replaces the analyzer with a Wollaston prism, for providing better image contrast. Images of a magnetic pattern obtained with both conventional and differential methods are observed for objective lenses that have different numerical apertures and magneto-optical disks with and without a birefringent substrate. The computer simulations and experimental results show that the use of this differential method improves the image contrast and provides excellent tolerance for defects of the optical system.

Temperature rise in a birefringent substrate caused by RF discharge plasma

Temperature rise in a birefringent substrate caused by RF discharge plasma

Temperature rise in a birefringent substrate caused by RF discharge plasma

Temperature rises of a birefringent substrate (LiNbO3) have been measured in an argon RF discharge plasma. The measurement method is based on monitoring the variation of natural birefringence with temperature by laser interferometry. Using this method, the dependence of substrate temperature rise on applied RF power and gas pressure has been investigated. The evaluation of the temperature curves shows that heat flux from the plasma toward the substrate is independent of time and temperature. The magnitude of the flux differs largely from the applied power, and is approximately 0.4% of the power. By measuring the electron density, electron temperature, and plasma potential with a Langmuir probe, the energy of the ions incident on the substrate is estimated. The ion flux toward the substrate is calculated from the energy of ions and is compared with the measured heat flux. The dependence on the applied power is in approximate agreement between those fluxes. The temperature distribution over the substrate thickness is simulated numerically using the finite difference method. © 1999 Scripta Technica, Electr Eng Jpn, 127(4): 9–17, 1999

Experimental Study on Heat Flux from an Argon RF Plasma Using Laser Interferometry Method

The plasma heat flow to a birefringent substrate (LiNbO3) in an argon rf discharge has been investigated with the help of a laser interferometry method. This method is based on monitoring the variation of natural birefringence with temperature by the interferometry. The evaluation of the temperature curve shows that heat flux from the plasma towards the substrate depends on which electrode the substrate is put on. While the value is about 8% of the applied power in the case of the substrate on the powered electrode, the heat flux decreases to less than 1% in the case of on the grounded electrode. Ion fluxes have been obtained from the measured values of plasma potential, electron density and electron temperature. In the case of low pressure the ion flux approximately agrees with the value of the heat flux. However it decreases with an increase in pressure, and is almost 35% of the heat flux at 200 mTorr. Gas temperature in the plasma has been measured using a thermocouple in order to investigate the influence of gas pressure on the heat flux by neutral particles. The result shows that the gas temperature increases by raising the gas pressure.

Eigenequations and Compact Algorithms for Bulk and Layered Anisotropic Optical Media: Reflection and Refraction at a Crystal-Crystal Interface

Eigenequations leading to compact algorithms for computing the optical properties of anisotropic media that may be stratified in the x-direction are described. For each medium a 4 × 4 matrix F of basis field vectors is determined as the eigenvectors of a 4 × 4 matrix form of Fresnel's equation. A minimum sort of the columns of F that is necessary for a birefringent cover or substrate separates basis vectors that carry power in the positive and negative x-directions respectively. A sorting procedure is discussed for the most complicated refractive index section in which the outer and inner sheets do not touch and the outer sheet has a well defined cusp. MATLAB code is provided for the implementation of basic routines.

Optimal design of polarizing beam splitters with a birefringent substrate

We present an optimal approach for designing polarizing beam splitters made of a sheet of birefringent material. The polarizing beam splitter is in the form of a transmission diffraction grating with a surface-relief structure of periodic sawtooth shape. We describe the necessary conditions for optimal design and derive the relevant equations for determining the structural parameters of the gratings. We demonstrate how to choose these parameters for a given substrate material to obtain the best result in the designed polarizing beam splitters. The influence of small variations in the parameters on grating performance is also investigated. It is shown that the performance of gratings is quite sensitive to small changes in the structural parameters.

RF放電プラズマによる基板の温度上昇

Temperature rises of a birefringent substrate (LiNbO3) have been measured in an argon RF discharge plasma. The measurement method is based on monitoring the variation of natural birefringence with temperature by laser interferometry. Using this method, the dependence of substrate temperature rise on applied RF power and gas pressure has been investigated. The evaluation of the temperature curves shows that heat flux from the plasma towards the substrate is independent of time and temperature. The magnitude of the flux differs largely from the applied power, and approximately 0.4‰ of the power. By measuring electron density, electron temperature and plasma potential with Langmuir probe, the energy of the ions incident on the substrate is estimated. The ion flux towards the substrate is calculated from the energy of ions and is compared with the measured heat flux. The dependence on the applied power is in approximate agreement between those fluxes. The temperature distribution over the substrate thickness is simulated numerically using the finite difference method.

Multilevel binary phase grating polarization device with a birefringent substrate

A multilevel binary phase grating polarization device that uses a birefringent material as the substrate is proposed, and the design is described. Based on the effect of combining double refraction with diffraction, this type of device can act as a polarizing beam splitter and has a number of advantages for practical use.